The Soviet Union Tests Its First Atomic Bomb

What happened

The Soviet Union detonated its first nuclear device — codenamed RDS-1, and dubbed 'Joe-1' in the West — years earlier than most American experts had predicted. President Truman announced the test to a shocked public in September 1949.

Why it matters

The Soviet bomb ended the American nuclear monopoly and launched the nuclear arms race that would shadow the entire Cold War.

Sources

• Office of the Historian, U.S. Department of State. Atomic Diplomacy · Reputable source